Preheat over to 375 degrees.
Sift the white flour, whole wheat flour, baking soda and salt together in a medium bowl and stir with a fork until they’re well combined.
Rub the butter in with your fingers until the mixture resembles coarse bread crumbs.2.
Form a well in the middle of the flour mixture and pour the buttermilk into the well.
Form your hand into a rigid claw and stir the buttermilk into the flour slowly but steadily in a spiral motion, starting in the middle and working outward.
The dough should be soft but not too wet or sticky.
(Add more buttermilk if necesary.)3.
Turn the dough out onto a floured board.
Flour your hands lightly, then shape the dough into a flat round about 2 inches high.
Cut a deep cross in the top of the loaf with a wet or floured knife, then bake for 45 to 60 minutes, or until nicely browned and the bottom of the loaf sounds hollow when tapped.